This is my thoughts on it: When you are crossing two different varieties there is always going to be a chance that they will be a little different. But if you breed say a barred rock to a barred rock, you are going to have barred rocks. There are throw back genes that can pop up from time to time, like a single combed wyandotte.
As for the new breeds, this is often how new breeds are introduced. But with doing this, once you get your crosses to a point that you are breeding for, they have to breed true. I dont know if I am making sense or not...
If you take your crossed male and females (now of the same variety/pattern) and cross them, the male chicks should nearly exactly like the dad and the female chicks should look nearly exactly like the female.
I hope I have made sense, if not someone will come and clarify that is way better with genetics than I am..